In a vehicle driven by an internal combustion engine, power is supplied from a power supply system for a vehicle load that uses a generator driven by the internal combustion engine as a power source, through a power supply line (a power supply bus), to various electrical loads provided in the vehicles. Many of the electrical loads of the vehicles are components that require to be driven for driving the vehicles.
Depending on types or uses of vehicles, electrical loads provided in a vehicle include a battery, an ignition device, a fuel pump, a fuel injection device, and a control device that controls them. For a vehicle incorporating a battery of 12 V, a power supply system for a vehicle load is comprised so as to output a DC voltage of 14 V required for charging the battery.
On the other hand, in vehicles such as ATVs (All Terrain Vehicles) or tractors, a power supply system for an external load that outputs AC power at a commercial frequency is sometimes provided in addition to a power supply system for a vehicle load, in order to allow electric tools or home appliances to be used outdoors.
Some proposals have been made on a power supply device incorporated in a vehicle driven by an internal combustion engine having two power supply systems. For example, Japanese Patent Application Laid-Open No. 50-36341 proposes a power supply device in which two types of voltage outputs are obtained by switching outputs of one generator with a transfer switch.
Japanese Patent Application Laid-Open No. 50-138529 proposes a power supply device in which different voltage outputs are obtained by using a transformer.
Further, Japanese Patent Application Laid-Open No. 60-161225 proposes a power supply device in which two types of voltage outputs are obtained by providing two generators in a vehicle.
FIG. 4 shows a construction example of a conventional power supply device incorporated in a vehicle driven by an internal combustion engine when two types of voltage outputs are obtained by providing two generators in a vehicle. In FIG. 4, a reference numeral 1 denotes a generator for driving on-vehicle electrical components driven by an internal combustion engine, and an output of the generator is converted into a DC output by a DC power supply circuit 2 having a rectification function and a voltage adjustment function, and then supplied through a power supply line 3 to a battery 4 and other electrical loads 5.
A reference numeral 6 denotes a synchronous generator for driving an external load, and an AC output at a commercial frequency obtained from an armature coil 6A is supplied across AC output terminals 7a, 7b to which the external load is connected. It is provided a field current control unit 8 that controls a field current to be flowed through a field coil 6B of the generator according to an output voltage of the armature coil 6A, and the control unit controls the field current so as to keep the output voltage of the armature coil 6A at a set value (for example, 100 V).
In order to keep an output frequency of the generator at 50 Hz or 60 Hz, rotational speed control means (not shown) is provided that controls a rotational speed of the engine so as to keep a rotational speed of the generator at 3000 r/min or 3600 r/min.
In this example, the generator 1 and the DC power supply circuit 2 constitute a power supply system for a vehicle load A1, and the generator 6 and the field current control unit 8 constitute a power supply system for an external load A2.
In the power supply device incorporated in a vehicle driven by an internal combustion engine shown in FIG. 4, the generator 1 has an output characteristic of generating an output enough to charge the battery 4 from an idling time of the engine. The battery 4 is sometimes omitted.
When the two types of voltage outputs are obtained by switching the outputs of one generator with the transfer switch as described in Japanese Patent Application Laid-Open No. 50-36341, the battery cannot be charged while the transfer switch is switched so as to drive the external load, which may run the battery down. Further, the battery is required in order to drive an electrical component such as an ignition device that requires to be driven for driving the engine, while the external load is driven, which is not suitable for a vehicle having no battery.
When the different voltage outputs are obtained by using the transformer as described in Japanese Patent Application Laid-Open No. 50-138529, a transformer of large mass requires to be provided in a vehicle, thus undesirably increasing a weight of the vehicle.
As shown in FIG. 4, if the two generators are used to constitute the power supply system for a vehicle load and the power supply system for an external load, the electrical component of the vehicle can be driven even when the external load is driven, thus solving the problem that the battery cannot be charged while the external load is driven. Further, the construction as shown in FIG. 4 allows a power supply system that drives the external load in a vehicle having no battery.
As shown in FIG. 4, when the two generators are provided, the generators are preferably made as small as possible for minimum increases in a size and a weight of the engine. However, the capacity of the generator 6 used in the power supply system for an external load depends on external loads to be driven, and thus a reduction in a size of the generator 6 is limited. In the construction in FIG. 4, the battery requires to be charged with the output of the generator 1 in the power supply system for a vehicle load from the idling time of the engine, and thus a large generator that generates a large output from a low speed time requires to be used as the generator 1. Therefore, the construction in FIG. 4 requires two large generators in the engine to increase the size and the weight of the engine. When the two generators are used as described above, the generator used in the power supply system for a vehicle load is preferably made as small as possible.
In order to reduce the size of the internal combustion engine, and reduce the number of parts for easy assembly, it is preferable that a generation coil provided in one generator is used to constitute two power supply systems: a power supply system for a vehicle load; and a power supply system for an external load. In this case, the increase in the size of the generator requires to be minimized.